The present invention relates to the growth of crystals from solutions, particularly to the isolation of seed crystals during processing of the crystal growth solution, and more particularly to a seed crystal protector which allows the seed to be present in the growth solution during processing thereof while preventing damage and dissolution to the seed.
In any method of solution crystal growth, the growth solutions must be filtered and overheated above the saturation point in order to remove all extraneous particles and dissolve crystal clusters which can become crystallization sources during growth of a single crystal. After these operations the seed crystal is introduced into the clean solution. This has been done in two different ways: 1) by introducing a seed fixed on a crystal holder into the tank which contains the processed solution, or 2) by introducing the solution into a tank which contains the seed.
In both of the above-referenced cases the cleanliness and stability of the solution obtained during filtration and overheating are reduced. New extraneous and crystalline particles come from the air, the crystal holder, walls of a dry tank, etc., and small crystalline clusters are formed due to local drying and cooling.
In addition, the seed itself has to be introduced at a temperature higher than the saturation point in order to dissolve crystalline particles which always exist on its surface. The higher the temperature the greater the probability of dissolving all crystalline particles. But at the same time the seed itself will be partially dissolved or even lost during this overheating operation, especially if a small seed is used in a large volume of solution as is often the case during the growth of large crystals, such as the KDP crystals for nonlinear optical devices, such as Pockel cells and frequency converters, weighing up to 3.5 kg.
Various crystal growing techniques have been developed to provide rapid growth of the crystals. These prior approaches are exemplified by N. P. Zaitseva et al., Study Of Rapid Growth Of KDP Crystals By Temperature Lowering, Kristallografiya, 36, 198-202, Jan. 1991; and J. Zachova et al., Application Of High Rate Crystal Growth Technique To Nucleic Acid Bases Single Crystals, SPIE, Vol. 1402, 216-222, 1990.
While these prior processes have greatly advanced the solution crystal growth technology, there is a need for protecting the seed crystal during processing of the growth solution and preventing contamination of the growth solution. This need is satisfied by the present invention which basically involves a seed protector which isolates the seed crystal during processing of the growth solution without removing the seed crystal from the tank containing the growth solution. The protector device basically involves a movable shaft having a sealed cup at one end which surrounds the seed crystal, and upon completion of the solution processing, the shaft is raised to expose the seed crystal to the growth solution.